The present invention relates to a heating boiler which can be fired by oil, gas or by solid fuel and which is provided with separate combustion chambers for the oil or gas burner and for the solid fuel. The combustion chambers are located in a common boiler water chamber and are connected with conduits for the combustion gases extending through the boiler water chamber and forming ancillary heating surfaces. The combustion gases are thereafter collected and drawn off by means of the usual flue.
In oil or gas-fired heating installations, especially with oil-firing, it is frequently desirable or necessary to be able also to burn solid fuels, especially wood, in the heating boiler of the installation. The setting up of an additional separate solid fuel-fired boiler, the provision of water connections coupling the boilers and of combustion as exhaust conduits connected with a common collector, is very expensive. Such interconnection of the boilers also requires the use of complex valving and control elements in the water circulating system and for the actuation of shut-off flaps in the exhaust system for the combustion gases to accommodate changeover from firing by one fuel to another. Therefore, double-fired boilers have been produced heretofore which contain separate combustion chambers for oil or gas-firing and for solid fuels, such chambers being located within a common boiler water jacket or boiler water space. These conventional double-fired boilers, however, always have common ancillary heating surfaces, for conveying the combustion gases from the burner firing combustion chamber and from the solid fuel combustion chamber. For example, it is known without having to increase the size of the usual heating boiler, to arrange a smaller oil or gas burner firing combustion chamber within a larger solid fuel combustion chamber and to exhaust the combustion gases by way of a connecting passage with the solid fuel combustion chamber. The combustion gases from the burner firing thus flow through the same exhaust conduits and ancillary heating surfaces in the heating boiler as do the combustion gases produced by the burning of the solid fuel in the solid fuel combustion chamber. These common ancillary heating surfaces of the known double-fired boilers have the disadvantage that ashes and other combustion residues such as always occur, for example, when wood is burned, accumulate on the ancillary heating surfaces used also for the combustion gases produced by the burner firing. This has a very disadvantageous and unfavorable effect upon the efficiency of the oil or gas-firing mode, which represents the normal type of firing in double-fired boilers and which requires the cleanest and most deposit-free ancillary heating surfaces for the achievement of high efficiency and economical fuel consumption. Deposits of ashes and other combustion residues as occurs in the burning of wood or other solid fuels can block the common combustion gas exhaust conduits and thus have extremely disadvantageous effects upon the pressure and flow conditions necessary for satisfactory burner operation. The common exhaust conduits of the known double-fired boiler would, therefore, have to be formed with increased unobstructed internal dimensions in order that after the burning of wood or other solid fuels it is possible to continue operation with burner firing without the need to first clean such conduits.
The invention thus deals with the problems of two-chamber heating boilers of the character described which avoids the disadvantages and drawbacks of presently known double-fired boilers.
The heating boiler according to the invention employs separate combustion gas exhaust systems connected to the two combustion chambers which pass completely separately from one another through the boiler water or compartment and terminate in a common combustion gas collector and flue for the heating boiler. Thus, both the combustion chambers or firing chambers and the ancillary heating surfaces for the oil or gas-firing and for the solid fuels are completely separate from one another upstream of the common collector and flue for the heating boiler. Fouling of the ancillary heating surfaces for the oil or gas-firing by the ash or other combustion residues occurring during the solid fuel firing is thus completely avoided, thereby insuring consistently high efficiencies and economy for the oil or gas-firing system. Moreover, the exhuast conduits and the ancillary heating surfaces formed by them may be constructed with the configuration, length and cross-sectional dimensions which are most expedient and favorable for the oil or gas-burner firing on the one hand and for the solid fuel firing on the other. The exhaust conduits for the solid fuel firing, for example, can be dimensioned to provide relatively large unobstructed internal passages in order to guarantee the longest possible maintenance-free firing time with solid fuels while the completely separate exhaust conduits for the oil and gas-burner firing can, in the manner favorable for this type of firing, comprise a plurality of finned pipes. Moreover, the separate combustion chambers and the completely separate exhaust systems can be arranged so that both the oil and gas-burner firing system and the solid fuel firing system can be fitted with only vertical conduits so that the burner firing system is also suitable for firing with atmospheric gas burners. The complete separation of the exhaust systems also offers a better possibility of forming the two combustion chambers independently of one another as is most favorable for the type of firing in each case. The combustion chamber for the burner firing, for example, can be of very large and deep dimensions to accommodate a particular specific flame reversal pattern and may be designed with dimensions for oil-firing to provide for optimum radiation transmission in order to reduce the production of unburnt oil derivatives which result in unpleasant odors, due to under-cooled combustion chamber zones. Irrespective of the formation of the combustion chamber and of the exhaust conduit system for the burner firing, the combustion chamber for the solid fuel firing can be of extraordinarily large dimensions in order to provide a large space for bulky solids such as wood. This latter combustion chamber and the connection of its exhaust conduits can be formed so that the combustion chamber is especially well adapted for the under-burning of long-flamed fuels such as wood, peat, cheap brown coal and the like, which are most commonly used for burning in the heating boiler.
It is one object of the invention to provide a heating boiler in which separate combustion chambers for oil or gas or for solid fuel located within a common boiler water compartment can be converted from solid fuel-firing to firing by oil or gas without the need for cleaning of the combustion gas exhaust conduits.
It is another object of the invention to provide a double-fired heating boiler which can be operated selectively in either its oil or gas-fired mode or by the burning of solid fuel without the need to increase the size of the common combustion gas exhaust conduits upstream of the flue to allow for ash and other residue of the solid fuel mode.
It is yet another object of the invention to provide a double-fired heating boiler in which space within the boiler water compartment is efficiently utilized for the passage therethrough of ancillary heat exchange surfaces.
In order that the invention may be more fully comprehended, it will now be described by way of example and in relation to a preferred embodiment with reference to the accompanying drawings.